/* falloc.c - The file space management routines for dbm. */
/* This file is part of GDBM, the GNU data base manager, by Philip A. Nelson.
Copyright (C) 1990, 1991 Free Software Foundation, Inc.
GDBM is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 1, or (at your option)
any later version.
GDBM is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with GDBM; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
You may contact the author by:
e-mail: phil@cs.wwu.edu
us-mail: Philip A. Nelson
Computer Science Department
Western Washington University
Bellingham, WA 98226
phone: (206) 676-3035
*************************************************************************/
#include "gdbmdefs.h"
/* The forward definitions for this file. See the functions for
the definition of the function. */
static avail_elem get_elem ();
static avail_elem get_block ();
static push_avail_block ();
static pop_avail_block ();
static adjust_bucket_avail ();
/* Allocate space in the file DBF for a block NUM_BYTES in length. Return
the file address of the start of the block.
Each hash bucket has a fixed size avail table. We first check this
avail table to satisfy the request for space. In most cases we can
and this causes changes to be only in the current hash bucket.
Allocation is done on a first fit basis from the entries. If a
request can not be satisfied from the current hash bucket, then it is
satisfied from the file header avail block. If nothing is there that
has enough space, another block at the end of the file is allocated
and the unused portion is returned to the avail block. This routine
"guarantees" that an allocation does not cross a block boundary unless
the size is larger than a single block. The avail structure is
changed by this routine if a change is needed. If an error occurs,
the value of 0 will be returned. */
long
_gdbm_alloc (dbf, num_bytes)
gdbm_file_info *dbf;
int num_bytes;
{
long file_adr; /* The address of the block. */
avail_elem av_el; /* For temporary use. */
/* The current bucket is the first place to look for space. */
av_el = get_elem (num_bytes, dbf->bucket->bucket_avail,
&dbf->bucket->av_count);
/* If we did not find some space, we have more work to do. */
if (av_el.av_size == 0)
{
/* Is the header avail block empty and there is something on the stack. */
if (dbf->header->avail.count == 0 && dbf->header->avail.next_block != 0)
pop_avail_block (dbf);
/* Get another full block from end of file. */
av_el = get_block (num_bytes, dbf);
dbf->header_changed = TRUE;
}
/* We now have the place from which we will allocate the new space. */
file_adr = av_el.av_adr;
/* Put the unused space back in the avail block. */
av_el.av_adr += num_bytes;
av_el.av_size -= num_bytes;
_gdbm_free (dbf, av_el.av_adr, av_el.av_size);
/* Return the address. */
return file_adr;
}
/* Free space of size NUM_BYTES in the file DBF at file address FILE_ADR. Make
it avaliable for reuse through _gdbm_alloc. This routine changes the
avail structure. The value TRUE is returned if there were errors. If no
errors occured, the value FALSE is returned. */
_gdbm_free (dbf, file_adr, num_bytes)
gdbm_file_info *dbf;
long file_adr;
int num_bytes;
{
avail_elem temp;
/* Is it too small to worry about? */
if (num_bytes <= IGNORE_SIZE)
return;
/* Initialize the avail element. */
temp.av_size = num_bytes;
temp.av_adr = file_adr;
/* Is the freed space large or small? */
if (num_bytes >= dbf->header->block_size)
{
if (dbf->header->avail.count == dbf->header->avail.size)
{
push_avail_block (dbf);
}
_gdbm_put_av_elem (temp, dbf->header->avail.av_table,
&dbf->header->avail.count);
dbf->header_changed = TRUE;
}
else
{
/* Try to put into the current bucket. */
if (dbf->bucket->av_count < BUCKET_AVAIL)
_gdbm_put_av_elem (temp, dbf->bucket->bucket_avail,
&dbf->bucket->av_count);
else
{
if (dbf->header->avail.count == dbf->header->avail.size)
{
push_avail_block (dbf);
}
_gdbm_put_av_elem (temp, dbf->header->avail.av_table,
&dbf->header->avail.count);
dbf->header_changed = TRUE;
}
}
if (dbf->header_changed)
adjust_bucket_avail (dbf);
/* All work is done. */
return;
}
/* The following are all utility routines needed by the previous two. */
/* Gets the avail block at the top of the stack and loads it into the
active avail block. It does a "free" for itself! */
static
pop_avail_block (dbf)
gdbm_file_info *dbf;
{
int num_bytes; /* For use with the read system call. */
long file_pos; /* For use with the lseek system call. */
avail_elem temp;
/* Set up variables. */
temp.av_adr = dbf->header->avail.next_block;
temp.av_size = ( ( (dbf->header->avail.size * sizeof (avail_elem)) >> 1)
+ sizeof (avail_block));
/* Read the block. */
file_pos = lseek (dbf->desc, temp.av_adr, L_SET);
if (file_pos != temp.av_adr) _gdbm_fatal (dbf, "lseek error");
num_bytes = read (dbf->desc, &dbf->header->avail, temp.av_size);
if (num_bytes != temp.av_size) _gdbm_fatal (dbf, "read error");
/* We changed the header. */
dbf->header_changed = TRUE;
/* Free the previous avail block. */
_gdbm_put_av_elem (temp, dbf->header->avail.av_table,
&dbf->header->avail.count);
}
/* Splits the header avail block and pushes half onto the avail stack. */
static
push_avail_block (dbf)
gdbm_file_info *dbf;
{
int num_bytes;
int av_size;
int av_adr;
int index;
long file_pos;
avail_block *temp;
avail_elem new_loc;
/* Caclulate the size of the split block. */
av_size = ( (dbf->header->avail.size * sizeof (avail_elem)) >> 1)
+ sizeof (avail_block);
/* Get address in file for new av_size bytes. */
new_loc = get_elem (av_size, dbf->header->avail.av_table,
&dbf->header->avail.count);
if (new_loc.av_size == 0)
new_loc = get_block (av_size, dbf);
av_adr = new_loc.av_adr;
/* Split the header block. */
temp = (avail_block *) alloca (av_size);
/* Set the size to be correct AFTER the pop_avail_block. */
temp->size = dbf->header->avail.size;
temp->count = 0;
temp->next_block = dbf->header->avail.next_block;
dbf->header->avail.next_block = av_adr;
for (index = 1; index < dbf->header->avail.count; index++)
if ( (index & 0x1) == 1) /* Index is odd. */
temp->av_table[temp->count++] = dbf->header->avail.av_table[index];
else
dbf->header->avail.av_table[index>>1]
= dbf->header->avail.av_table[index];
/* Update the header avail count to previous size divided by 2. */
dbf->header->avail.count >>= 1;
/* Free the unneeded space. */
new_loc.av_adr += av_size;
new_loc.av_size -= av_size;
_gdbm_free (dbf, new_loc.av_adr, new_loc.av_size);
/* Update the disk. */
file_pos = lseek (dbf->desc, av_adr, L_SET);
if (file_pos != av_adr) _gdbm_fatal (dbf, "lseek error");
num_bytes = write (dbf->desc, temp, av_size);
if (num_bytes != av_size) _gdbm_fatal (dbf, "write error");
}
/* Get_elem returns an element in the AV_TABLE block which is
larger than SIZE. AV_COUNT is the number of elements in the
AV_TABLE. If an item is found, it extracts it from the AV_TABLE
and moves the other elements up to fill the space. If no block is
found larger than SIZE, get_elem returns a size of zero. This
routine does no I/O. */
static avail_elem
get_elem (size, av_table, av_count)
int size;
avail_elem av_table[];
int *av_count;
{
int index; /* For searching through the avail block. */
avail_elem val; /* The default return value. */
/* Initialize default return value. */
val.av_adr = 0;
val.av_size = 0;
/* Search for element. List is sorted by size. */
index = 0;
while (index < *av_count && av_table[index].av_size < size)
{
index++;
}
/* Did we find one of the right size? */
if (index >= *av_count)
return val;
/* Ok, save that element and move all others up one. */
val = av_table[index];
*av_count -= 1;
while (index < *av_count)
{
av_table[index] = av_table[index+1];
index++;
}
return val;
}
/* This routine inserts a single NEW_EL into the AV_TABLE block in
sorted order. This routine does no I/O. */
_gdbm_put_av_elem (new_el, av_table, av_count)
avail_elem new_el;
avail_elem av_table[];
int *av_count;
{
int index; /* For searching through the avail block. */
int index1;
/* Is it too small to deal with? */
if (new_el.av_size <= IGNORE_SIZE)
return FALSE;
/* Search for place to put element. List is sorted by size. */
index = 0;
while (index < *av_count && av_table[index].av_size < new_el.av_size)
{
index++;
}
/* Move all others up one. */
index1 = *av_count-1;
while (index1 >= index)
{
av_table[index1+1] = av_table[index1];
index1--;
}
/* Add the new element. */
av_table[index] = new_el;
/* Increment the number of elements. */
*av_count += 1;
return TRUE;
}
/* Get_block "allocates" new file space and the end of the file. This is
done in integral block sizes. (This helps insure that data smaller than
one block size is in a single block.) Enough blocks are allocated to
make sure the number of bytes allocated in the blocks is larger than SIZE.
DBF contains the file header that needs updating. This routine does
no I/O. */
static avail_elem
get_block (size, dbf)
int size;
gdbm_file_info *dbf;
{
avail_elem val;
/* Need at least one block. */
val.av_adr = dbf->header->next_block;
val.av_size = dbf->header->block_size;
/* Get enough blocks to fit the need. */
while (val.av_size < size)
val.av_size += dbf->header->block_size;
/* Update the header and return. */
dbf->header->next_block += val.av_size;
/* We changed the header. */
dbf->header_changed = TRUE;
return val;
}
/* When the header already needs writing, we can make sure the current
bucket has its avail block as close to 1/2 full as possible. */
static
adjust_bucket_avail (dbf)
gdbm_file_info *dbf;
{
int third = BUCKET_AVAIL / 3;
avail_elem av_el;
/* Can we add more entries to the bucket? */
if (dbf->bucket->av_count < third)
{
if (dbf->header->avail.count > 0)
{
dbf->header->avail.count -= 1;
av_el = dbf->header->avail.av_table[dbf->header->avail.count];
_gdbm_put_av_elem (av_el, dbf->bucket->bucket_avail,
&dbf->bucket->av_count);
dbf->bucket_changed = TRUE;
}
return;
}
/* Is there too much in the bucket? */
while (dbf->bucket->av_count > BUCKET_AVAIL-third
&& dbf->header->avail.count < dbf->header->avail.size)
{
av_el = get_elem (0, dbf->bucket->bucket_avail, &dbf->bucket->av_count);
_gdbm_put_av_elem (av_el, dbf->header->avail.av_table,
&dbf->header->avail.count);
dbf->bucket_changed = TRUE;
}
}